1. Field of the Invention
This invention relates to electro-mechanical relays and, more particularly, to electro-mechanical relay apparatus including a built-in attenuator network.
2. History of the Prior Art
Electro-mechanical relays have been used in electronic circuits for as long as such circuits have been manufactured. Such relays utilize a mechanical connector which is opened and closed to make contact between two points in a electric circuit. Although many such relays have been replaced by electronic switches which may be made very small and thus may be placed within the tiny circuits of modern electronics, many situations exist where the electrical-performance of an electro-mechanical relay is superior to that of the electronic switch. For example, an electro-mechanical relay can achieve a flat amplitude response well into the gigahertz frequency range and still have a response down to direct current. The power handling capabilities of an electro-mechanical switch greatly exceed those of electronic switches. For these and many other reasons, electro-mechanical switches are useful in many situations.
Moreover as the circuitry associated with electro-mechanical relays has become smaller and smaller, so have the electro-mechanical relays. Today, such relays often fit into packages of less than 0.05 cubic inches.
One type of mechanical switch provides two current paths through electronic circuitry so that two independent operations may be selected One specific use of such a switch is to provide a signal to a piece of electronic equipment in one position of the switch or, alternatively, to attenuate a signal for some other within the equipment in the other position of the switch. For example, a receiver for electronic signals may use a mechanical switch to activate either the receiver or built-in self-test equipment which assures that the receiver is operating correctly. However, the typical signal generated for self-testing a radio receiver is much too large to use, on the order of five milliwatts, and simply saturates the equipment (which is designed to detect small signals) producing no useful information. In order to utilize this locally generated signal with the self-testing circuitry, it is necessary to drastically attenuate the signal. Consequently, attenuator circuits have been designed to reduce the value of the testing signal to a value such as five micro-microwatts which would be typical of a received signal. Other values of attenuation may also be used in particular circuits. Such an attenuated signal may then be routed by the electro-mechanical relays and used for self testing. Many other uses exist for an electro-mechanical relay and circuitry capable of providing both a straight connection and an attenuated path.
Such attenuators operate efficiently but have a number of draw backs. First, the typical attenuator circuitry is much too large, ten times or greater than the volume of the relays with which they are associated, to conveniently fit within the same package as the receiver circuitry; so it is inconvenient to build them into the receiver without substantially enlarging the package. Second, because of their size, such attenuator circuits cannot be used with higher frequency receivers. The length of the connectors used offers too much residual impedance for use in high frequency circuitry. For example, receivers operating at about 1.5 gigahertz are about the upper limit for use with such attenuators.